When I delete movies from my ipad, I can't load them again from itunes. Why?

I have an older ipad. When I load a bunch of movies onto my ipad, they load fine. When I get done watching a movie, I delete it from the ipad. What I've discovered is that once I delete a movie form the ipad, it will not reload in the future should I decide to want to watch it again.

I make sure that the movie is still on my hard drive, I can click on it in itunes and watch it on the computer, yet it won't load onto the ipad.

Suggestions? Does itunes keep a memory of deleted items and prevent reloading? If so, how do I wipe that memory and start from scratch?